原位肝胆系转化在非酒精性脂肪性肝病肝纤维化启动过程中的作用及其机制研究

Liver fibrosis is clinically validated to be the most important risk factor for disease progression and serious outcomes of nonalcoholic fatty liver disease (NAFLD). It is crucial to understand the initiating mechanism underlying fibrogenesis in NAFLD. However, current hypotheses cannot well address the characteristic tempo-spatial pattern of histological fibrosis progressing in adult NAFLD patients. Based on our data of full-spectrum fibrosis analysis in clinical biopsies and murine model as well as the understanding of current progress in basic research of chronic liver injury-related liver regeneration, we propose our hypothesis that, in the setting of lipid over-load, hepatocytes in zone 3 might have adaptive changes associated with the pathological regeneration and consequently, fibrogenesis in form of ductular reaction. Our idea was then preliminarily verified by the data of in vitro hepatocyte lipid-culture model, showing there was a typical change in expression of master genes indicating hepatobiliary lineage transition. Therefore, we propose, by leveraging current models and tools of fibrosis detection, to comprehensively identify the features of the lipid-induced hepatobiliary transition and its association with fibrogenesis from the perspectives of morphological, phenotypical, molecular and bona fide functional levels, respectively. We will also analyze the cellular identities of ductular reaction in the transition. The proposed study may provide a novel hypothesis complementary to current understanding of NAFLD pathophysiology.

肝纤维化是预测非酒精性脂肪性肝病（NAFLD）疾病进展的首要指标。NAFLD纤维化启动机制对于理解和早期诊断疾病进展具有重要价值，但目前各类假说不能合理解释NAFLD纤维化起始在组织学水平的时空特征。我们基于前期实验对NAFLD全程病变临床活检样本和小鼠模型的纤维化组织学特征的测量数据，并基于对当前领域关于慢性损伤肝再生机制研究进展的理解，提出假设：NAFLD纤维化起始损伤可能与脂质异常负荷过程出现zone 3肝细胞适应性再生有关。该假设又由体外肝细胞模型因持续脂质蓄积诱发肝胆系特征分子表达转化得以验证。为此，计划继续利用肝细胞和小鼠模型，系统分析脂质蓄积引起肝胆系转化的细胞表型、形态学和功能学变化，及其分子机制特征；利用小鼠模型观察肝胆系转化与纤维化发生在肝小叶出现的空间、数量和时间的相关性，并鉴定其胆管反应类细胞学特征。本研究内容将为探索NAFLD纤维化启动机制提供新思路。

肝纤维化是非酒精性脂肪性肝病（NAFLD）疾病进展的首要预测指标。NAFLD纤维化启动机制对于理解和早期诊断疾病进展具有重要价值，但目前各类假说不能合理解释NAFLD纤维化起始在组织学水平的时空特征。基于前期实验NAFLD全程病变临床活检样本和小鼠模型的纤维化组织学特征的测量数据，以及关于慢性损伤肝再生机制研究进展，本项目创新性地提出，脂质持续高负荷可能引起肝细胞直接发生胆系转化，进而增加胆管反应和后续纤维化发生的危险性，即为NAFLD肝纤维化启动的重要机制。项目展开的主要研究内容包括利用高脂负荷肝细胞模型，系统分析脂质蓄积引起肝胆系转化的细胞表型、形态学和功能学变化，及其分子机制特征；利用多种诱因的NASH小鼠模型观察肝胆系转化与纤维化发生在肝小叶出现的空间、数量和时间的相关性及其分子通路机制，并分析其胆管反应类细胞学特征；以及在病理组织样本验证分析肝胆系转化与纤维化发生的相关性。实验发现确认了NAFLD条件下脂质负荷持续增加在早期可以诱发肝细胞发生肝胆系转化，肝细胞胆系表型的出现对下游纤维化重要作用分子的表达有活化作用；不同诱因引起的NAFLD模型中，肝组织中胆系标志物分布均与早期肝纤维化发生在时间和空间上具有一致性；YAP-Notch通路是NAFLD早期脂肪负荷增加引起肝胆系转化的重要机制通路。这些数据发现为理解NAFLD肝纤维化启动机制和下一步寻找可控靶点提供了重要线索、奠定了新的探索方向。与此同时，我们在技术上还建立了NAFLD肝组织纤维化空间特征分析系统，可以精确测量肝纤维化分布变化，其应用价值已经实验模型和临床队列初步验证。